1. Field of the Invention
The present invention relates to a linear driving device, in which a movable body is linearly moved.
2. Related Art
Patent Document 1 discloses a linear driving device, in which an end of a driving shaft is fixed to a vibration member, with a metal vibrator having elasticity being superimposed on and fixed to a piezoelectric element, and by vibrating the driving shaft in an axial direction, a movable body in frictional contact with the driving shaft is linearly moved.
Moreover, in this type of conventional linear driving device, in general, as shown in FIG. 4, an end face of a driving shaft 51 having a cylindrical shape is fixed to the center of a plane of a plate-like vibrator 55 that is superimposed on a piezoelectric element 53.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-259345
In recent years, in this type of linear driving device, it is required to reduce the size of the device, while obtaining predetermined driving torque without changing level of driving power and characteristic of the piezoelectric element.
In order to address such a demand, the present inventors have conducted studies and experiments, and have found as a result that, in a vibration member composed of a piezoelectric element and a vibrator, torque acting on a movable body frictionally contact with a driving shaft mainly depends on deformation of the vibrator that elastically deforms due to mass of the driving shaft and expansion and contraction of the piezoelectric element.
In other words, torque F acting on the movable body due to vibration of the driving shaft can be generally obtained by the expression, F=ma. Here, m is mass, and a is acceleration.
Therefore, where the mass of the driving shaft is m, the acceleration a is acceleration when the vibrator elastically deforms; accordingly, the present inventors have conducted studies aiming at reducing the size of the vibration member, while obtaining predetermined acceleration (elastic deformation) a in the vibrator, with little change of the mass m of the driving shaft.
An object of the present invention is to provide a linear driving device, in which size reduction of the device can be achieved, while obtaining predetermined driving torque without changing level of driving power and characteristic of the piezoelectric element.